In nuclear industry and nuclear research environments, a contamination risk is posed by the presence of tritium, typically in the form of tritiated water vapour. Tritium filters are therefore used in air-purifying respirators (in addition to whole-body protection as appropriate) to protect workers in tritium-contaminated environments. An air-purifying respirator must therefore either remove the tritiated water vapour or tritium from the air before it is inhaled by the worker, or else substitute the tritiated water vapour or air with normal water vapour air. As is known in the art, one type of filter medium used to filter tritium vapour in air-purifying respirators is a corrugated or pleated paper, which captures tritium by adsorption. However, to be effective in filtering tritium, the paper medium must be wetted.
A contaminated environment is not necessarily contaminated by a single contaminant. Airborne tritium or tritiated vapour may be accompanied by various types of particulates which can also be harmful to workers in the environment. Particulate filters, such as HEPA filters, can be used to filter out such contaminants. A tritium paper filter is insufficient to filter the particulates filtered by a HEPA filter, and a HEPA filter does not provide protection against tritium for any significant duration. HEPA filters, and other types of filters for respiratory protection, are ineffective or have reduced effectiveness when they are wetted; moisture in the HEPA filter medium can saturate the filter medium, blocking airflow, and may damage the filter medium itself.